&#39;Thermal spring&#39; magnetic recording media for writing using magnetic and thermal gradients

ABSTRACT

A magnetic recording system is provided having a write head employing a combination of magnetic write field gradient and thermal gradient to write data on a ‘thermal spring’ magnetic recording media. The write head comprises a magnetic element using a write current to induce a magnetic write field at the magnetic media and a thermal element using a very small aperture laser to heat a portion of the media. The thermal spring magnetic media comprises first and second stacks providing two exchange coupled ferromagnetic layers having different Curie temperatures. The first stack has a high magneto-crystalline anisotropy, a relatively low saturation magnetization and a low Curie temperature. The second stack has a relatively low magneto-crystalline anisotropy, a high saturation magnetization and a high Curie temperature. The magnetic field gradient and the thermal gradient are arranged to substantially overlap at the trailing edge of the heated portion of the magnetic media allowing data at high density with high thermal stability to be recorded on the rapidly cooling thermal spring magnetic recording media.

CROSS REFERENCE TO RELATED APPLICATION

[0001] U.S. patent application Ser. No. ______ docket numberSJO919990221US1, entitled THERMALLY ASSISTED MAGNETIC RECORDING SYSTEMAND METHOD OF WRITING USING MAGNETIC AND THERMAL GRADIENTS, was filed onthe same day and owned by a common assignee.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to magnetic recording systems forwriting information signals on a magnetic medium and, in particular, toa magnetic recording system employing a combination of magnetic writefield gradient and thermal gradient to increase the areal density ofmagnetic recording, and to a ‘thermal spring’ magnetic recording mediafor recording information with such systems.

[0004] 2. Description of the Related Art

[0005] Moving magnetic storage devices, especially magnetic disk drives,are the memory device of choice. This is due to their expandednon-volatile memory storage capability together with a relatively lowcost. Thin film magnetic read/write heads are used for reading andwriting magnetically coded data stored on a magnetic storage medium suchas a magnetic disk.

[0006] Magnetic disk drives are information storage devices whichutilize at least one rotatable magnetic media disk having concentricdata tracks defined for storing data, a read/write transducer forreading data from and/or writing data to the various data tracks, aslider for supporting the transducer adjacent the data tracks typicallyin a flying mode above the storage media, a suspension assembly forresiliently supporting the slider and the transducer over the datatracks, and a positioning actuator coupled to thetransducer/slider/suspension combination for moving the transduceracross the media to the desired data track and maintaining thetransducer over the data track center line during a read or a writeoperation. The transducer is attached to or is formed integrally withthe slider which supports the slider above the data surface of thestorage disk by a cushion of air, referred to as an air bearing,generated by the rotating disk.

[0007] There is a continuing strongly-felt need for increasing the datastorage density in the magnetic media of the storage disks. Most effortsto increase magnetic storage density involve techniques for increasingthe areal bit density in the magnetic storage medium. In rotatingmagnetic disk drives, the areal density is the product of the number offlux reversals, or bits, per unit length along a data track and thenumber of tracks available per unit length of disk radius. In currenthigh areal density storage systems the bit density is in the range of300-500×10³ bits/inch and the track density is in the range of 20-36×10³tracks/inch resulting in an areal density of about 10-18 Gbits/in².Advances to areal densities of 40-100 Gbits/in² are probably achievablewith the prior art technology by implementing careful control of mediamicrostructure in order to ensure thermal stability of the stored dataand to keep media noise within acceptable limits.

[0008] However, there is a problem with the prior art magnetic recordingsystems and the magnetic media as areal density is further increased todensities greater than about 100 Gbits/in². As the track densityincreases, it becomes increasingly difficult to maintain the transducercentered over the very narrow data track during read and writeoperations. As the bit density along the track increases, a morefundamental problem arises due to the small size of the bits causinginstability of the bit magnetization due to thermal fluctuations. As thebit size decreases, the energy of thermal fluctuations becomescomparable to the stored magnetic energy which is given by the productof the switching volume and the magneto-crystalline anisotropy of thematerial. This results in a decay of the bit magnetization and loss ofthe stored data.

[0009] Therefore, there is a need for a magnetic recording system thatprovides increased areal density of data with improved thermal stabilityand for a method of writing data on high areal density magnetic media insuch a magnetic recording system.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to disclose a magneticrecording system employing a combination of magnetic write fieldgradient and thermal gradient to write data on a magnetic recordingdisk.

[0011] It is another object of the present invention to dislose amagnetic recording system combining a magnetic write field gradient anda thermal gradient to write data on a magnetic disk having a highmagneto-crystalline anisotropy resulting in an increased areal recordingdensity.

[0012] It is yet another object of the present invention to disclose amagnetic recording system combining a magnetic write field gradient anda thermal gradient to write data on a magnetic disk, wherein themagnetic write field gradient and the thermal gradient are spatially andtemporally coincident on the write area of the magnetic disk during thewrite operation.

[0013] It is still another object of the present invention to disclose a‘thermal spring’ magnetic recording medium for writing data at highareal density using a magnetic write field gradient combined with athermal gradient.

[0014] It is a further object of the present invention to disclose amethod of writing data at high areal density with a combined magneticwrite field gradient and a thermal gradient.

[0015] In accordance with the principles of the present invention, thereis disclosed a magnetic recording system having a write head comprisinga magnetic element and a thermal element and a magnetic recording diskincluding a thermal spring magnetic recording media. The thermal springmagnetic recording media comprises first and second stacks in alaminated structure providing two exchange coupled ferromagnetic layershaving different Curie temperatures. The first stack has a highmagneto-crystalline anisotropy and a low Curie temperature. The secondstack has a relatively low magneto-crystalline anisotropy, a highsaturation magnetization and a high Curie temperature.

[0016] The write head comprises a magnetic element for providing amagnetic field gradient at the magnetic recording medium and a thermalelement for providing a thermal gradient at the magnetic recordingmedium spatially and temporally coincident with the magnetic fieldgradient. The thermal element is a very small aperture laser (VSAL), asolid state laser device having a very small aperture in a metallicreflector layer for emitting a pulse of high intensity light through awrite gap of the magnetic element. Alternatively, continuous wave (cw)light may be used for very thin or well heat sunk magnetic media forwhich the cooling rate after the heat source passes through issufficiently high. The magnetic element comprises the metallicreflective layer of the VSAL electrically insulated from the solid statelaser by a dielectric layer. A write current pulse is directed throughthe metallic reflective layer perpendicular to the direction of motionof the magnetic media relative to the read/write head to produce amagnetic field pulse with the field extending into the region betweenthe the aperture and the magnetic media. Alternatively, the magneticelement may be a inductive write head having first and secondferromagnetic pole pieces separated by a write gap and magneticallycoupled at a back gap and a conductive coil for inducing a magneticfield flux in the pole pieces resulting in a magnetic field gradient atthe write gap. The pulse of light from the VSAL impinges on and isabsorbed by the magnetic media resulting in rapid heating of themagnetic media in the write gap region. As the magnetic media movesrelative to the write gap, a thermal gradient at the trailing edge ofthe heated spot in the magnetic media is coincident spatially andtemporally with the magnetic field gradient in the media generated bythe write current pulse.

[0017] The magnetic field gradient provided by the write current pulsewill be steepest in the vicinity of the trailing edge of the lightaperture. While the width of the write track is mainly defined by thesize and shape of the aperture, that is, by the temperature profile andgradient created by the light spot, the transition length is defined bythe overlapping thermal and magnetic field gradients. In this region ofoverlapping thermal and magnetic field gradients, the coercivity of themagnetic media is thermally reduced sufficiently to allow switching ofthe magnetization by the magnetic field gradient followed by rapidcooling back to the high coercivity state due to the steep thermalgradient and the motion of the media.

[0018] To avoid thermal instabilities of the stored magnetic data, aminimal stability ratio of stored magnetic energy K_(U)V to thermalenergy k_(B)T of K_(u)V/k_(B)T of about 60 is required, where K_(U) isthe magneto-crystalline anisotropy of the magnetic media, V is themagnetic switching volume, k_(B) is the Boltzmann constant and T is thetemperature of the media. Having successfully switched the magneticmedia by heating the transition region so as to exceed its write energythreshold, it is necessary to rapidly cool the transition region inorder to prevent thermal instabilities from degrading the newmagnetization state. By arranging to substantially overlap the trailingedges of the temperature and magnetic field gradients produced by theVSAL light pulse and the write current pulse through the metallicreflective layer, respectively, the transition region cools by diffusiveprocesses sufficiently rapidly to maintain its magnetization.

[0019] The above, as well as additional objects, features and advantagesof the present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a fuller understanding of the nature and advantages of thepresent invention, as well as the preferred mode of use, referenceshould be made to the following detailed description read in conjunctionwith the accompanying drawings. In the following drawings, likereference numerals designate like or similar parts throughout thedrawings.

[0021]FIG. 1 is a simplified diagram of a magnetic recording disk drivesystem using the write head and disk media of the present invention;

[0022]FIG. 2a is a perspective view, not to scale, of a read/write headof the present invention fixed on the trailing end of a slider;

[0023]FIG. 2b is a vertical cross-section view, not to scale, of anembodiment of the read/write head of the present invention.

[0024]FIG. 2c is a sectional view, not to scale, of a section A-A of theread/write head of FIG. 2b;

[0025]FIG. 2d is an air bearing surface view, not to scale, of theread/write head of FIG. 2b;

[0026]FIG. 2e is an air bearing surface view, not to scale, of aread/write head having an alternate location of the aperture of theVSAL;

[0027]FIG. 2f is an air bearing surface view, not to scale, of aread/write head having an alternate shape of the conductive layer on theemitting surface of the VSAL;

[0028]FIG. 2g is an air bearing surface view, not to scale, of aread/write head having a second alternate shape of the conductive layeron the emitting surface of the VSAL;

[0029]FIG. 2h is an air bearing surface view, not to scale, of anembodiment of a read/write head having a magnetic layer on the emittingsurface of the VSAL;

[0030]FIG. 2i is a vertical cross-section view, not to scale, of anembodiment of a read/write head having a magnetic layer on the emittingsurface of the VSAL;

[0031]FIG. 3a is a cross-sectional view, not to scale, of a highmagneto-crystalline anisotropy magnetic media for use with theread/write head of the present invention;

[0032]FIG. 3b is a graph of the temperature dependence of themagneto-crystalline anisotropy field H_(K) for a high K_(U) magneticmedia material;

[0033]FIG. 4a is a cross-sectional view, not to scale, of a firstembodiment of a thermal spring magnetic media of the present invention;

[0034]FIG. 4b is a cross-sectional view, not to scale, of an alternateembodiment of a thermal spring magnetic media of the present invention;

[0035]FIG. 5a is a graph of the magneto crystalline anisotropy and theCurie temperature of Co/Pt multilayers as functions of the Co layerthickness for a fixed Pt layer thickness of 10 Å.

[0036]FIG. 5b is a graph of the temperature dependence of the coercivityof multilayer (12 repetitions) stacks of Co/Pt having different Co layerthicknesses.

[0037]FIG. 5c is a graph of the temperature dependence of themagneto-crystalline anisotropy field H_(K) for an embodiment of athermal spring magnetic media of the present invention;

[0038]FIG. 6a is a cross-sectional view, not to scale, of a secondembodiment of a thermal spring magnetic media of the present invention;

[0039]FIG. 6b is a cross-sectional view, not to scale, of a thirdembodiment of a thermal spring magnetic media of the present invention;

[0040]FIG. 7 is a graph of the time dependence of the write field H_(W)and of the temperature and magneto-crystalline anisotropy field H_(K) ofa thermal switch magnetic media material heated by a nanosecondtimescale VSAL pulse; and

[0041]FIG. 8 is a graph of the thermal and magnetic field gradientsmodeled for a 100 nm square aperture separated 5 nm from the magneticmedia surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] The following description is the best embodiment presentlycontemplated for carrying out the present invention. This description ismade for the purpose of illustrating the general principles of thepresent invention and is not meant to limit the inventive conceptsclaimed herein.

[0043] Referring now to FIG. 1, there is shown a disk drive 100embodying the present invention. As shown in FIG. 1, at least onerotatable magnetic disk 112 is supported on a spindle 114 and rotated bya disk drive motor 118. The magnetic recording media on each disk is inthe form of an annular pattern of concentric data tracks (not shown) onthe disk 112.

[0044] At least one slider 113 is positioned on the disk 112, eachslider 113 supporting one or more magnetic read/write heads 121 of thepresent invention. As the disks rotate, the slider 113 is moved radiallyin and out over the disk surface 122 so that the heads 121 may accessdifferent portions of the disk where desired data is recorded. Eachslider 113 is attached to an actuator arm 119 by means of a suspension115. The suspension 115 provides a slight spring force which biases theslider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator 127. The actuator as shown in FIG. 1 may be avoice coil motor (VCM). The VCM comprises a coil movable within a fixedmagnetic field, the direction and speed of the coil movements beingcontrolled by the motor current signals supplied by a controller 129.

[0045] During operation of the disk storage system, the rotation of thedisk 112 generates an air bearing between the slider 113 (the surface ofthe slider 113 which includes the head 121 and faces the surface of thedisk 112 is referred to as an air bearing surface (ABS)) and the disksurface 122 which exerts an upward force or lift on the slider. The airbearing thus counter-balances the slight spring force of the suspension115 and supports the slider 113 off and slightly above the disk surfaceby a small, substantially constant spacing during normal operation.

[0046] The various components of the disk storage system are controlledin operation by control signals generated by the control unit 129, suchas access control signals and internal clock signals. Typically, thecontrol unit 129 comprises logic control circuits, storage chips and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123 and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position the slider 113 to the desired data track onthe disk 112. Read and write signals are communicated to and from theread/write heads 121 by means of the recording channel 125. Recordingchannel 125 may be a partial response maximum likelihood (PMRL) channelor a peak detect channel. The design and implementation of both channelsare well known in the art and to persons skilled in the art. In thepreferred embodiment, recording channel 125 is a PMRL channel.

[0047] The above description of a typical magnetic disk storage system,and the accompanying illustration of FIG. 1 are for representationpurposes only. It should be apparent that disk storage systems maycontain a large number of disks and actuator arms, and each actuator armmay support a number of sliders.

[0048] The present invention is now described with reference to FIGS.2a, 2 b, 2 c and 2 d. FIG. 2a is a perspective view, not to scale, of aread/write head 200 according to a preferred embodiment of the presentinvention. The read/write head 200 comprises a write head 202 fixed to atrailing end 203 of a slider 201 and a read head 204 fixed to the writehead 202. The slider 201 supports the read/write head 200 so that an ABS209 is separated from a data track 205 on a magnetic media movingrelative to the read/write head as indicated schematically by the arrowhead. FIG. 2b shows a schematic vertical cross-section view, not toscale, of the read/write head 200 suspended above a disk surface 122comprising a magnetic recording media 207 moving relative to theread/write head 200 as indicated by the arrow head 211. The write head202 comprises a very small aperture laser (VSAL) 206 having an emittingsurface 208 at the ABS 209 coated with a fully reflecting multilayerthin film structure 210 with a very small aperture 212 through which thelaser light is emitted. A suitable VSAL has been described by Partovi etal., Applied Physics Letters, Volume 75, No. 11, p. 1515. Thispublication describes a high power laser light source for near-fieldoptics applications having light emitting apertures in the range of50-400 nm square. The small size of the VSAL (typical size is 750 μm×300μm×150 μm) allows it to be supported on a slider to form part of aread/write head. Since the spacing between the emitting surface of theVSAL and the magnetic recording media is small (in the range of 10-100nm) compared to the wavelength of the emitted light (in the range of600-1000 nm), the write head is operating well within the near-fieldoptics regime. A multilayer thin film structure 210 comprises a fullyreflective conductive layer 214 separated from the emitting surface 208by an insulating layer 216. Alternatively, reflective conductive layer214 may include a reflective layer on the insulating layer 216 and aseparate conductive layer deposited over the reflective layer. The readhead 204 comprises a thin film MR sensor 218 having a front edge 220located at the ABS 209. The MR sensor 218 is sandwiched between firstand second nonmagnetic gap layers 222 and 224 which are in turnsandwiched between first and second magnetic shield layers 226 and 228.The read head 204 is preferably formed by thin film vacuum depositionprocesses known to the art on an interface layer 230 deposited on a sidesurface 232 perpendicular to the ABS 209. The MR sensor 218 ispreferably a giant magnetoresistive (GMR) or a magnetic tunnel junction(MTJ) sensor for reading magnetic signals well known to the art.

[0049]FIG. 2c shows a sectional view, not to scale, of a section A-A ofthe read/write head 200 of FIG. 2b. The side surfaces 234 of the VSAL206 are coated with insulating layers 236 separating conductive layers238 from the VSAL 206 side surfaces. The conductive layers 238 contactconductive layer 214 to form a continuous conductive layer around theside surfaces 234 and the emitting surface 208 of the VSAL 206. Acurrent source 240 is connected via leads 242 to the conductive layers238 to provide a write current I_(W) flowing through the conductivelayer 214 during a write operation.

[0050]FIG. 2d shows an ABS view, not to scale, of the read/write head200 indicating the positioning of the aperture 212 of the VSAL 206 andthe front edge 220 of the MR sensor 218 relative to a data track 205moving relative to the read/write head 200 as indicated by the arrowhead.

[0051] It will be apparent that the aperture 212 need not be centered onemitting surface 208, but may, alternatively, be located nearer, asshown in FIG. 2e, or further from the side surface 234. Also, theconductive layer 214 may, alternatively, be shaped so as to direct andconcentrate the write current I_(W) relative to the VSAL aperture 212 soas to maximize the write current induced magnetic field extending to thedata track 205 on the magnetic media in the write region. Two exemplaryshapes for conductive layer 214 are shown in FIGS. 2f and 2 g.

[0052] The current needed to provide a write field at the surface of adisk 112 separated from the ABS 209 by a distance of 10 nm has beenestimated for the embodiment of the write head 202 shown in FIG. 2f. Fora conductive layer 214 having a length L=10 μm perpendicular to the datatrack 205, a width W=1 μm parallel to the data track and a thicknessT=100 nm, a write current I_(w)=15 mamp produces a write fieldH_(w)=3000 Oe. In order to meet the requirements for fast switching, theresistance of the conductive layer 214 should be kept low (less thanabout 10 ohms) so that a material having a resistivity of the order of10 μohm-cm or less is needed. Therefore the conducting layer 214 may beformed of any high conductivity metal such as, for example, copper,silver, and aluminum, however, in order to also have high corrosionresistance conductive layer 214 is preferably formed of gold, platinumor palladium.

[0053]FIGS. 2h and 2 i show another embodiment of the invention having awrite head 202 differing from the write heads shown in FIGS. 2a-2 g inhaving an inductive magnetic element 240 to provide a write fieldinstead of the conductive layer 214. The inductive magnetic element 240comprises a ferromagnetic pole structure 250 and a pancake coilstructure 254 through which write current flows to induce a magneticwrite field in the ferromagnetic pole structure 250 as is well known inthe art. In this embodiment, a reflective layer 215 having an aperture212 is deposited over the emitting surface. A soft ferromagnetic polestructure 250 is deposited over the reflective layer 215 for providing amagnetic write field across the write gap 256 at the aperture 212. Thesoft ferromagnetic pole structure 250 abutts a ferromagnetic pole 251formed on the side surface 232 of the VSAL 206. The coil structure 254isolated by insulation layers 252 is deposited over and under theferromagnetic pole 251 as is well known to the art of inductive writehead design. Leads (not shown) are connected to the ends of coilstructure 254 for providing a write current. The read head 204 may bedeposited over the ferromagnetic pole 251 and coil structure 254. Theferromagnetic pole 251 and ferromagnetic pole structure 250 arepreferably formed Ni—Fe, Fe—Co or other high moment, high Curietemperature ferromagnetic materials.

[0054] A write operation using the read/write head 200 of the presentinvention to write on a magnetic material with a very highmagneto-crystalline anisotropy K_(U) suitable for very high densitymagnetic data will now be described. The magnetic field pulse requiredfor writing a transition into the magnetic recording media is producedby a short current pulse I_(w) directed via conductive layers 238through the metallic reflective layer 214 perpendicular to the directionof motion of the magnetic media relative to the read/write head 200 toproduce a magnetic field pulse with the field extending into the regionbetween the the aperture 212 and the magnetic media. However, because ofthe high magneto-crystalline anisotropy K_(U) of the magnetic recordingmedia, the media switching field H_(o) will be too high for switching bythe magnetic field pulse at ambient temperature. The media switchingfield H_(o) is proportional to the ratio K_(U)/M_(S), where M_(S) is thesaturation magnetization.

[0055] To reduce the media switching field H_(o) to a sufficiently lowvalue for the current generated magnetic field pulse to switch themagnetization of the recording media, a thermal pulse is simultaneouslyor nearly simultaneously applied to the recording media by means of apulse of light from the VSAL 206, or alternatively, by cw light from theVSAL passing over the recording media at a high linear velocity. Thelight from the VSAL 206 impinges on and is absorbed by the magneticmedia resulting in rapid heating of the magnetic media in the write gapregion. The localized heating of the magnetic media results in adecrease of the magneto-crystalline anisotropy K_(U) and themagnetization saturation M_(S). Generally, K_(U) and M_(S) are functionsof temperature and decrease with temperature according to K_(U)(T)∝{M_(S)(T)}^(n) such that H_(O)=K_(U)/M_(S) also decreases withincreasing temperature (for example, n=3 for cubic materials and n=10for hexagonal materials).

[0056]FIG. 3a shows the structure of a Co/Pt multilayer magnetic mediamaterial 300, an illustrative example of a high K_(U) magnetic materialsuitable for use with the read/write head of the present invention. TheCo/Pt multilayer of this embodiment comprises a stack 302 of alternatinglayers of Co 306 having a thickness of about 2 Å and layers of Pt 308having a thickness of about 10 Å. Typically, the stack 302 includes inthe range of 4-15 repetitions of the Co and Pt layers 306 and 308. Thestack 302 is deposited over an underlayer 320 deposited on a substrate322 to help promote the desired texture and crystalline structure of thelayers in the stack 302. An overlayer 324 is deposited over the stack302 for protection from oxidation and mechanical damage.

[0057]FIG. 3b shows the temperature dependence of H_(K) for an exemplaryCoPt multilayer of the kind shown in FIG. 3a. Since, in order to write atransition, the switching field H_(O) cannot exceed the write fieldcapability of the recording head which is about 5000-10000 Oe, theswitching region in the magnetic media of this example must be heated bythe light pulse from the VSAL 206 to a temperature of about 275° C.Because the slope dH_(K)/dT is very steep in the vicinity of theswitching field and the Curie temperature T_(C) of the media cannot beexceeded for magnetic writing to be possible, well-controlled heating ofthe media by the light pulse is critical for successful writing to beachieved.

[0058] In order to overcome the need for critical temperature controlduring the current pulse write operation, a novel magnetic recordingmedia has been invented for use with the read/write head of the presentinvention. In this embodiment, the magnetic media, referred to as a‘thermal spring’ magnetic recording media, comprises two stacks ofalternating layers of magnetic and nonmagnetic material. The basic ideaof the thermal spring magnetic recording media will now be brieflydescribed. Thermal spring media are ferromagnetic recording mediacomprising a first stack and a second stack (layer stacks) in laminarcontact with each other, or alternatively, having a suitable nonmagneticspacer layer disposed between the first stack and the second stack. Thefirst stack, with a relatively low Curie temperature T_(C1), has a roomtemperature coercivity too high for writing with the field from aconventional magnetic recording write head. The second stack, with ahigh Curie temperature T_(C2), has a lower coercivity suitable forwriting with a conventional magnetic recording write head. During thewrite process, the media is locally heated by a thermal element of thewrite head to a temperature approximately equal to or slightly greaterthan T_(C1), thereby reducing its coercivity. The desired data bitpattern is then recorded in the second stack by the field from amagnetic element of the write head. Immediately after writing, the mediacools as it moves out of the heating zone of the thermal element and asthe first stack cools below its Curie temperature T_(C1) it becomesferromagnetic again and the bit pattern is “copied” or transferred fromthe second stack to the first stack by means of a magnetic exchangeinteraction (exchange spring mechanism). On further cooling, theanisotropy/coercivity of the first layer returns to its original highvalue thereby providing the desired long-term stability of themagnetically recorded data.

[0059]FIG. 4a shows the layer structure of a thermal spring magneticrecording media 400 for use with the read/write head of the presentinvention. The thermal spring media 400 includes a first stack 402comprising first magnetic layers 406 of cobalt (Co) having a thicknessin the range of 1-8 Å interleaved with first nonmagnetic layers 408 ofplatinum (Pt), or alternatively of palladium (Pd), having a thickness inthe range of 1-25 Å and a second stack 404, in laminar contact with thefirst stack, comprising second magnetic layers 410 of Co having athickness in the range of 10-50 Å interleaved with second nonmagneticlayers 412 of palladium (Pd), or alternatively of platinum (Pt), havinga thickness in the range of 1-25 Å. The first stack 402 is made of aplurality of repetitions of the layers of Co and Pt materials,preferably 4-15 repetitions. The second stack 404 is made of a pluralityof repetitions of the layers of Co and Pd materials, preferably 1-4repetitions. Alternatively, the first and second magnetic layers 406 and410 may be made of ferromagnetic cobalt-based alloys such as Co—Pt—Cr—B,Co—Pt—Cr, Co—Cr, Co—Pd—Cr—B, Co—Pt—Cr—Nb, Co—Pd—Cr—Nb and Co—Pd—Cr.Alternatively, a nonmagnetic spacer layer may be disposed between thefirst stack 402 and the second stack 404.

[0060] A magnetic recording disk using the thermal spring media 400 ismade by depositing an underlayer or underlayers 420 on a substrate 422followed by deposition of alternating layers of Co and Pt to form thefirst stack 402 on the underlayer 420. The second stack 404 is thendeposited over the first stack 402 by alternately depositing layers ofCo and Pt to the desired number of repetitions. A protective overlayer424 is deposited over the second stack 404 to provide corrosionresistance and mechanical protection. The thermal spring media 400 maybe fabricated using thin film deposition processes well known to theart.

[0061] In FIG. 4a, the thermal spring media 400 is shown with the secondstack 404 having the lower magneto-crystalline anisotropy and the higherCurie temperature deposited over the first stack 402 having the highermagneto-crystalline anisotropy and the lower Curie temperature.Alternatively, as shown in FIG. 4b, the order of the first and secondstacks 402 and 404 may be inverted so that the first stack 402 isdeposited over the second stack 404. In this alternative embodiment, thelayer structure of a magnetic recording disk using the media 400 issubstrate/underlayer/second stack/first stack/overlayer.

[0062] The first and second stacks 402 and 404 of the thermal springmedia 400 provide two exchange coupled ferromagnetic layers havingdifferent Curie temperatures. The first stack 402 has a highmagneto-crystalline anisotropy K_(U1), a relatively low saturationmagnetization M_(S1) and a low Curie temperature T_(C1). The secondstack 404 has a relatively low magneto-crystalline anisotropy K_(U2), ahigh saturation magnetization M_(S2) and a high Curie temperatureT_(c2). Assuming K(T)/K₀=(M(T)/M₀)³, to first order H_(K) of the bylayeris H_(K)=(3K_(U1)+K_(U2))/(3M_(S1)+M_(S2)).

[0063]FIG. 5a shows experimental data for the dependence on thickness ofthe Co layers of the effective magneto crystalline anisotropy K_(U)(curve 502) and the Curie temperature T_(C) (curve 504) of Co/Ptmultilayers for a fixed Pt layer thickness in the stack of 10 Å. Thedata for effective Ku is from Lin et al., JMMM 93, (1991) p. 194-206. Bychoosing the thickness of the Co layers in the Co/Pt multilayer stack,stacks having desired values of K_(U) and T_(C) may be obtained.

[0064]FIG. 5b shows experimental data for the temperature dependence ofthe coercivity H_(C) for multilayer (12 repetitions) stacks of Co/Pthaving 2 Å thick Co layers and 10 Å thick Pt layers in a first stack(curve 506) and 12 Å thick Co layers and 10 Å thick Pt layers in asecond stack (curve 508). By choosing a Co layer thickness of 2 Å, thedata shows that a Co/Pt stack having a high coercivity and low Curietemperature (curve 506) is obtained while choosing a Co layer thicknessof 12 Å yields a Co/Pt stack having a relatively low coercivity andhigher Curie temperature (curve 508).

[0065]FIG. 5c shows an exemplary temperature dependence of theanisotropy field H_(K) for the thermal spring media 400. The Curietemperature T_(C1) of the high anisotropy stack 402 is chosen to to be100-350° C. lower than the Curie temperature T_(C2) of the lowanisotropy stack 404. The temperature region between T_(C2) and T_(C1)provides a broad temperature range with nearly uniform anisotropy fieldto which the thermal pulse generated by the light from the VSAL 206 mayheat the media during the write process without driving the media into anonmagnetic state.

[0066]FIG. 6a shows the layer structure of a second embodiment of athermal spring magnetic recording media 600 for use with the read/writehead of the present invention. The thermal spring media 600 comprises abilayer 601 formed of a thick first magnetic layer 606 of highmagneto-crystalline anisotropy K_(U1), low Curie temperature T_(C1)material and an adjacent thin second magnetic layer 608 of low K_(U2),high saturation magnetization M_(S2), high Curie temperature T_(C2)material in laminar contact with the first layer. The first magneticlayer 606 is made of the L1₀ phase of Fe—Pt—Ni where a small amount ofNi is added to reduce T_(C) to the desired level. Table 1 is datashowing the effect of Ni concentration on the magneto-crystallineanisotropy K_(U) and the Curie temperature T_(C) of L1₀ materials. Thefirst magnetic layer 606 of Fe—Pt—Ni has a thickness of approximately 60Å. Alternatively, the first magnetic layer 606 may be formed of othergranular, high anisotropy alloys such as the L1₀ phases of Fe—Pt, Co—Ptand Co—Pd. The second magnetic layer 608 is made of Co—Pt—Cr having athickness of approximately 20 Å deposited over the first magnetic layer606. Alternatively, the second magnetic layer 608 may be formed of otherlow Ku, high Ms, high T_(C) materials including Co—Pt, Co—Pt—Cr,Co—Pt—Cr—Nb, Co—Pt—Cr—B, Co—Pd, Co—Pd—Cr, Co—Pd—Cr—Nb and Co—Pd—Cr—Balloys. TABLE 1 Magneto-crystalline anisotropy and Curie temperature ofL1₀ materials Composition K_(U) (erg/cc) T_(C) (° C.) Fe₅₅Pt₄₅ 7 × 10⁷500 Fe₄₅Pt₄₅Ni₁₀ 3 × 10⁷ 400 Fe₃₅Pt₄₅Ni₂₀ 2 × 10⁶ 300

[0067] The magnetic media 600 is formed on a substrate 602 on which anunderlayer 604 is deposited. The underlayer 604 is a seed layer whichmay be chosen to promote granular structure of the bilayer 601 havingeither in-plane or out-of-plane easy axis alignment for longitudinal orperpendicular recording applications, respectively. The first and secondmagnetic layers 606 and 608 are deposited sequentially over theunderlayer 604 and a protective overlayer 610 is deposited over thesecond magnetic layer 608. Alternatively, as discussed above withreference to FIGS. 4a and 4 b, the order of the first and secondmagnetic layers 606 and 608 shown in FIG. 6a may be inverted with secondmagnetic layer 608 deposited over first magnetic layer 606.

[0068] The first and second layers 606 and 608 of the thermal springmedia 600 provide two exchange coupled ferromagnetic layers havingdifferent Curie temperatures. As discussed above with reference to thethermal spring magnetic media 400, the first magnetic layer 606 has ahigh magneto-crystalline anisotropy K_(U1), a relatively low saturationmagnetization M_(S1) and a low Curie temperature T_(C1). The secondmagnetic layer 608 has a relatively low magneto-crystalline anisotropyK_(U2), a high saturation magnetization M_(S2) and a high Curietemperature T_(c2). Assuming K(T)/K₀=(M(T)/M₀)³, to first order H_(K) ofthe bilayer is H_(K)=(3K_(U1)+K_(U2))/(3M_(S1)+M_(S2)). FIG. 5c shows anexemplary temperature dependence of the anisotropy field H_(K) for thethermal spring media 600. The Curie temperature T_(C1) of the highanisotropy layer 606 is chosen to be 100-350° C. lower than the Curietemperature T_(C2) of the low anisotropy layer 608. The temperatureregion between T_(C2) and T_(C1) provides a broad temperature range withnearly uniform anisotropy field to which the thermal pulse generated bythe light from the VSAL 206 may heat the media during the write processwithout driving the media into a nonmagnetic state.

[0069]FIG. 6b shows the layer structure of a third embodiment of athermal spring magnetic recording media 620 for use with the read/writehead of the present invention. The thermal spring media 620 comprises athick first magnetic layer 622 of a granular L1₀ phase of Fe—Pt—Nihaving a thickness of approximately 60 Å and an adjacent thin stack 624,in laminar contact with the first magnetic layer, made of a plurality ofrepetitions, preferably 1-4 repetitions, of second magnetic layers 626of Co having a thickness in the range of 10-50 Å interleaved withnonmagnetic layers 628 of Pd, or alternatively Pt, having a thickness inthe range of 1-25 Å. Alternatively, the first magnetic layer 622 may beformed of other granular, high anisotropy alloys such as the L1₀ phasesof Fe—Pt, Co—Pt and Co—Pd. The second magnetic layers 626 may be made offerromagnetic cobalt-based alloys such as Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr,Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb, Co—Pd—Cr—B and Co—Pd—Cr. The first magneticlayer 622 and the stack 624 provide two exchange coupled ferromagneticlayers having different Curie temperatures. The first magnetic layer 622has high magneto-crystalline anisotropy K_(U1), relatively lowsaturation magnetization M_(S1) and a low Curie temperature T_(C1). Thestack 624 of alternating magnetic and nonmagnetic layers has lowmagneto-crystalline anisotropy K_(U2), high saturation magnetizationM_(S2) and a high Curie temperature T_(C2). The Curie temperature T_(C1)of the first magnetic layer 622 is chosen to be 100-350° C. lower thanthe Curie temperature T_(C2) of the stack 624. Alternatively, the orderof the first magnetic layer 622 and the stack 624 in FIG. 6b may beinverted with the stack 624 deposited on the underlayer 604 and thefirst magnetic layer 622 deposited over the stack 624.

[0070]FIG. 7 shows the time dependence of the temperature of anexemplary thermal spring media due to heating by the light from the VSAL206 and the concomitant variation of the anisotropy field H_(K) of themedia caused by the thermal pulse. At the trailing end 702 of thethermal pulse, the media cools rapidly to a write temperature T_(W) justbelow T_(C1) where the gradient dH_(K)/dT is a maximum. By adjustment ofthe heater power provided by the VSAL 206, the time when the temperatureT_(W) is reached may be chosen to coincide with the onset of the highestmagnetic field gradient dH/dx|_(magnetic) from the current generatedmagnetic field pulse. By temporally overlapping the magnetic fieldgradient dH/dx|_(magnetic) with the thermal field gradientdH_(K)/dx|_(thermal)=dH_(K)/dT.dT/dx, the transition width of thewritten data can be shortened as will be described hereafter.

[0071] A process for writing data on a thermal spring magnetic recordingmedia using the read/write head of the present invention will now bedescribed with reference to FIG. 7. A portion of the magnetic recordingmedia passing under the aperture on the thermal element emitting surfaceis rapidly heated to a temperature between the first and second Curietemperatures T_(C1) and T_(C2) (in the range of 310-400° C. for anexemplary thermal spring media having T_(C1)=300° C.) due to absorptionof light emitted by the VSAL. The heating step may be implemented byusing a short pulse of light from the VSAL or, alternatively, by usingcontinuous wave (cw) emission from the VSAL and relying on the rapidmotion of the media relative to the write head to provide a thermalgradient in the media at the trailing edge of the aperture. As theheated portion of the media moves past the aperture it cools rapidlybelow T_(C1) resulting in a large thermal gradient at the trailing end702 of the thermal pulse and a rapid increase in the anisotropy fieldH_(K). A magnetic write field pulse 704 is turned on by providing awrite current pulse to the write element of the write head. Preferably,the steep magnetic field gradient 706 at the trailing edge of themagnetic write field pulse 704 overlaps and is coincident with themaximum gradient 701 of the anisotropy field H_(K). The magnetic writefield pulse 704 switches the magnetization of the magnetic recordingmedia just prior to the increase of the anisotropy field H_(W) above themaximum magnetic write field H_(W,max) due to the rapid cooling of themedia. Overlapping of the magnetic field gradient and the thermalgradient results in the shortest write transition widths in the media.Further cooling of the magnetic recording media results in a furtherincrease of the anisotropy field H_(K) and the magnetocrystallineanisotropy K_(U) providing very high thermal stability for the recordedmagnetic data.

[0072] The write field gradient produced by the short write currentpulse will be steepest in the vicinity of the trailing edge of the lightaperture. While the data bit width will be defined mainly by the sizeand shape of the aperture, i.e. by the temperature profile and gradientcreated by the light spot, the data bit length will be defined by theoverlapping thermal and magnetic field gradients. To first order, themagnetic field gradient dH_(K)/dx|_(magnetic) due to the rising magneticfield produced by the write current pulse adds to the thermal fieldgradient dH_(K)/dx|_(thermal)=dH_(K)/dT.dT/dx due to the rapid mediacooling at the trailing edge of the VSAL pulse. This additive effect ofthe magnetic and thermal gradients of the anisotropy field H_(K) allowsvery short transition widths to be achieved.

[0073] An example illustrating the improved transition widths expectedfrom the combined magnetic field and thermal field gradients is nowdescribed with reference to FIGS. 5c and 8. FIG. 5c shows thetemperature dependence of H_(K) for an exemplary high anisotropymagnetic media consisting of grains with a rectangular switching fielddistribution of +/−10% around an applied field H═H_(K)/2=4000 G.Assuming a write head which delivers a rise of the magnetic write fieldfrom 0 to 8000 G in a distance of 200 nm, a magnetic gradientdH_(K)/dx|_(magnetic)=40 G/nm is obtained. With the above graindistribution, the write transition width a_(W) for magnetic only writingis a_(W)=H_(K)/(dH_(K)/dx)|_(HW+/−)10%=20 nm as shown by curve 802 inthe upper portion of FIG. 8.

[0074] For the case of combined magnetic field and thermal fieldwriting, the slope of H_(K) around the writing temperature is estimatedfrom FIG. 5c to be dH_(K)/dT=600 G/° C. For illustrative purposes, thethermal gradient is assumed to be dT/dx=0.07° C./nm so thatdH_(K)/dx|_(thermal)=dH_(K)/dT.dT/dx=(600 G/° C.) (0.07° C./nm)=40 G/nmis approximately equal to the magnetic gradient dH_(K)/dx|_(magnetic).Referring to the lower portion of FIG. 8, switching again starts at 3600Oe, but since the media is cooling rapidly and thus raising H_(K) at theleading edge, the thermal and magnetic gradients add and the 3600 Oespot is now only 5 nm away from the 4000 Oe spot as shown by curve 804compared to the 10 nm distance for magnetic field only writing shown bycurve 802 resulting in a transition width a_(W)=10 nm for combinedmagnetic and thermal writing.

[0075] We have estimated the magnitude of thermal gradients and thustransition widths that can be achieved. Typical magneto-optical mediaknown to the art have thermal gradients of about dT/dx=0.25° C./nmwhich, for a slope of H_(K) around the writing temperature of 600°C./nm, results in dH_(K)/dx|_(thermal)=dH_(K)/dT.dT/dx=(600 G/° C.)(0.25° C./nm)=150 G/nm and a transition width a_(W)=4.2 nm. Forthermally optimized media with a localized laser spot much steeperthermal gradients are possible. From simple heat dissipationconsiderations we estimate dT/dx=5° C./nm is achievable resulting indH_(K)/dx|_(thermal)=3000 G/nm and a_(W)=0.25 nm.

[0076] While the present invention has been particularly shown anddescribed with reference to the preferred embodiments, it will beunderstood by those skilled in the art that various changes in form anddetail may be made without departing from the spirit, scope and teachingof the invention. Accordingly, the disclosed invention is to beconsidered merely as illustrative and limited only in scope as specifiedin the appended claims.

We claim:
 1. A magnetic recording media, comprising: a first stackcomprising a plurality of repetitions of first magnetic layersinterleaved with first nonmagnetic layers, wherein said first stack hasa first Curie temperature and a first magneto-crystalline anisotropy;and a second stack comprising a plurality of repetitions of secondmagnetic layers interleaved with second nonmagnetic layers, said secondstack in laminar contact with said first stack, and wherein said secondstack has a second Curie temperature greater than said first Curietemperature and said second stack has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy.
 2. The magnetic recording media recitedin claim 1, wherein said first magnetic layers are made of cobalt. 3.The magnetic recording media recited in claim 1, wherein said firstmagnetic layers are chosen from a group of materials consisting of Co,Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb, Co—Pd—Cr—B andCo—Pd—Cr.
 4. The magnetic recording media recited in claim 3, whereinsaid first magnetic layers have a thickness in the range of 1-8 Å. 5.The magnetic recording media recited in claim 1, wherein said firstnonmagnetic layers are made of platinum or palladium.
 6. The magneticrecording media recited in claim 5, wherein said first nonmagneticlayers have a thickness in the range of 1-25 Å.
 7. The magneticrecording media recited in claim 1, wherein said second magnetic layersare made of cobalt.
 8. The magnetic recording media recited in claim 1,wherein said second magnetic layers are chosen from a group of materialsconsisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb,Co—Pd—Cr—B and Co—Pd—Cr.
 9. The magnetic recording media recited inclaim 8, wherein said second magnetic layers have a thickness in therange of 10-50 Å.
 10. The magnetic recording media recited in claim 1,wherein said second nonmagnetic layers are made of platinum orpalladium.
 11. The magnetic recording media recited in claim 10, whereinsaid second nonmagnetic layers have a thickness in the range of 1-25 Å.12. The magnetic recording media recited in claim 1, wherein saidplurality of repetitions of first magnetic layers interleaved with firstnonmagnetic layers is in the range of 4-15.
 13. The magnetic recordingmedia recited in claim 1, wherein said plurality of repetitions ofsecond magnetic layers interleaved with second nonmagnetic layers is inthe range of 1-4.
 14. The magnetic recording media recited in claim 1,wherein the first Curie temperature of the first stack is in the rangeof 100-350° C. lower than the second Curie temperature of the secondstack.
 15. A magnetic recording media, comprising: a first magneticlayer made of a granular L1₀ phase of Fe—Pt or Co—Pt alloys, whereinsaid first magnetic layer has a first Curie temperature and a firstmagneto-crystalline anisotropy; and a second magnetic layer made ofCo—Pt or Co—Pd alloys, said second magnetic layer in laminar contactwith said first magnetic layer, and wherein said second magnetic layerhas a second Curie temperature greater than said first Curie temperatureand said second magnetic layer has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy.
 16. The magnetic recording media recitedin claim 15, wherein said first magnetic layer is made of Fe—Pt—Ni. 17.The magnetic recording media recited in claim 15, wherein the firstmagnetic layer has a thickness of about 60 Å.
 18. The magnetic recordingmedia recited in claim 15, wherein the second magnetic layer is made ofCo—Pt—Cr.
 19. The magnetic recording media recited in claim 15, whereinthe second magnetic layer has a thickness of about 20 Å.
 20. Themagnetic recording media recited in claim 15, wherein the second Curietemperature is in the range of 100-350° C. higher than the first Curietemperature.
 21. A magnetic recording media, comprising: a firstmagnetic layer made of a granular L1₀ phase of Fe—Pt or Co—Pt alloys,wherein said first magnetic layer has a first Curie temperature and afirst magneto-crystalline anisotropy; and a stack comprising a pluralityof repetitions of second magnetic layers interleaved with nonmagneticlayers, said stack in laminar contact with said first magnetic layer,wherein said stack has a second Curie temperature greater than saidfirst Curie temperature and wherein said stack has a secondmagneto-crystalline anisotropy smaller than said firstmagneto-crystalline anisotropy.
 22. The magnetic recording media recitedin claim 21, wherein the first magnetic layer is made of Fe—Pt—Ni. 23.The magnetic recording media recited in claim 21, wherein the firstmagnetic layer has a thickness of about 60 Å.
 24. The magnetic recordingmedia recited in claim 21, wherein said second magnetic layers are madeof cobalt.
 25. The magnetic recording media recited in claim 21, whereinsaid second magnetic layers are chosen from a group of materialsconsisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb,Co—Pd—Cr—B and Co—Pd—Cr.
 26. The magnetic recording media recited inclaim 21, wherein said second magnetic layers have a thickness in therange of 10-50 Å.
 27. The magnetic recording media recited in claim 21,wherein said nonmagnetic layers are made of platinum or palladium. 28.The magnetic recording media recited in claim 21, wherein saidnonmagnetic layers have a thickness in the range of 1-25 Å.
 29. Themagnetic recording media recited in claim 21, wherein said plurality ofrepetitions of second magnetic layers interleaved with nonmagneticlayers is in the range of 1-4.
 30. The magnetic recording media recitedin claim 21, wherein the first Curie temperature of the first magneticlayer is in the range of 100-350° C. lower than the second Curietemperature of the stack.
 31. A magnetic recording media, comprising: afirst magnetic layer having a first magneto-crystalline anisotropy and afirst Curie temperature; and a second magnetic layer having a secondmagneto-crystalline anisotropy and a second Curie temperature, whereinsaid second magneto-crystalline anisotropy is smaller than said firstmagneto-crystalline anisotropy and said second Curie temperature isgreater than said first Curie temperature, and wherein said secondmagnetic layer is in laminar contact with said first magnetic layer. 32.The magnetic recording media as recited in claim 31, wherein said firstmagnetic layer is made of Fe—Pt—Ni.
 33. The magnetic recording media asrecited in claim 31, wherein said first magnetic layer has a thicknessin the range of 60 Å.
 34. The magnetic recording media as recited inclaim 31, wherein said second magnetic layer is made of Co—Pt—Cr. 35.The magnetic recording media as recited in claim 31, wherein said secondmagnetic layer has a thickness of about 20 Å.
 36. The magnetic recordingmedia as recited in claim 31, wherein said first magnetic layer ischosen from a group of materials consisting of Fe—Pt, Co—Pt and Co—Pd.37. The magnetic recording media as recited in claim 31, wherein saidsecond magnetic layer is chosen from a group of materials consisting ofCo—Pt, Co—Pt—Cr, Co—Pt—Cr—Nb, Co—Pt—Cr—B, Co—Pd, Co—Pd—Cr, Co—Pd—Cr—Nband Co—Pd—Cr—B.
 38. The magnetic recording media recited in claim 31,wherein the first Curie temperature of the first magnetic layer is inthe range of 100-350° C. lower than the second Curie temperature of thesecond magnetic layer.
 39. A magnetic recording media, comprising: alayer means for providing a first stack in laminar contact with a secondstack, wherein said first stack has a first magnetocrystallineanisotropy greater than a second magnetocrystalline anisotropy of saidsecond stack; and wherein said first stack has a first Curie temperaturesmaller than a second Curie temperature of said second stack.
 40. Themagnetic recording media recited in claim 39, wherein the first Curietemperature of the first stack is in the range of 100-350° C. lower thanthe second Curie temperature of the second stack.
 41. A magneticrecording media, comprising: a layer means for providing a first stackhaving a first Curie temperature and a first magneto-crystallineanisotropy; a layer means for providing a second stack having a secondCurie temperature larger than the first Curie temperature and a secondmagneto-crystalline anisotropy having a magnitude smaller than the firstmagneto-crystalline anisotropy; and a spacer layer disposed between thefirst stack and the second stack.
 42. The magnetic recording mediarecited in claim 41, wherein the first Curie temperature of the firststack is in the range of 100-350° C. lower than the second Curietemperature of the second stack.
 43. A magnetic recording diskcomprising: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a first stack comprising a plurality of repetitions of first magneticlayers interleaved with first nonmagnetic layers, wherein said firststack has a first Curie temperature and a first magneto-crystallineanisotropy; and a second stack comprising a plurality of repetitions ofsecond magnetic layers interleaved with second nonmagnetic layers, saidsecond stack in laminar contact with said first stack, and wherein saidsecond stack has a second Curie temperature greater than said firstCurie temperature and said second stack has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy.
 44. The magnetic recording disk recitedin claim 43, wherein said first magnetic layers are chosen from a groupof materials consisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb,Co—Pd—Cr—Nb, Co—Pd—Cr—B and Co—Pd—Cr.
 45. The magnetic recording diskrecited in claim 43, wherein said second magnetic layers are chosen froma group of materials consisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr,Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb, Co—Pd—Cr—B and Co—Pd—Cr.
 46. The magneticrecording disk recited in claim 43, wherein said first nonmagneticlayers are made of platinum or palladium.
 47. The magnetic recordingdisk recited in claim 43, wherein said second nonmagnetic layers aremade of platinum or palladium.
 48. A magnetic recording disk comprising:a substrate; an underlayer adjacent to the substrate; an overlayer; anda magnetic recording media disposed between the underlayer and theoverlayer, said magnetic recording media comprising: a first magneticlayer made of a granular L1₀ phase of Fe—Pt or Co—Pt alloys, whereinsaid first magnetic layer has a first Curie temperature and a firstmagneto-crystalline anisotropy; and a second magnetic layer made ofCo—Pt or Co—Pd alloys, said second magnetic layer in laminar contactwith said first magnetic layer, and wherein said second magnetic layerhas a second Curie temperature greater than said first Curie temperatureand said second magnetic layer has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy.
 49. The magnetic recording disk recitedin claim 48, wherein said first magnetic layer is made of Fe—Pt—Ni. 50.The magnetic recording disk recited in claim 48, wherein the secondmagnetic layer is made of Co—Pt—Cr.
 51. A magnetic recording diskcomprising: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a first magnetic layer made of a granular L1₀ phase of Fe—Pt or Co—Ptalloys, wherein said first magnetic layer has a first Curie temperatureand a first magneto-crystalline anisotropy; and a stack comprising aplurality of repetitions of second magnetic layers interleaved withnonmagnetic layers, said stack in laminar contact with said firstmagnetic layer, wherein said stack has a second Curie temperaturegreater than said first Curie temperature and wherein said stack has asecond magneto-crystalline anisotropy smaller than said firstmagneto-crystalline anisotropy.
 52. The magnetic recording disk recitedin claim 51, wherein the first magnetic layer is made of Fe—Pt—Ni. 53.The magnetic recording disk recited in claim 51, wherein said secondmagnetic layers are chosen from a group of materials consisting of Co,Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb, Co—Pd—Cr—B andCo—Pd—Cr.
 54. The magnetic recording disk recited in claim 51, whereinsaid nonmagnetic layers are made of platinum or palladium.
 55. Amagnetic recording disk comprising: a substrate; an underlayer adjacentto the substrate; an overlayer; and a magnetic recording media disposedbetween the underlayer and the overlayer, said magnetic recording mediacomprising: a first magnetic layer having a first magneto-crystallineanisotropy and a first Curie temperature; and a second magnetic layerhaving a second magneto-crystalline anisotropy and a second Curietemperature, wherein said second magneto-crystalline anisotropy issmaller than said first magneto-crystalline anisotropy and said secondCurie temperature is greater than said first Curie temperature, andwherein said second magnetic layer is in laminar contact with said firstmagnetic layer.
 56. The magnetic recording disk as recited in claim 55,wherein said first magnetic layer is chosen from a group of materialsconsisting of Fe—Pt, Fe—Pt—Ni, Co—Pt and Co—Pd.
 57. The magneticrecording disk as recited in claim 55, wherein said second magneticlayer is chosen from a group of materials consisting of Co—Pt, Co—Pt—Cr,Co—Pt—Cr—Nb, Co—Pt—Cr—B Co—Pd, Co—Pd—Cr, Co—Pd—Cr—Nb and Co—Pd—Cr—B. 58.A magnetic recording disk comprising: a substrate; an underlayeradjacent to the substrate; an overlayer; and a magnetic recording mediadisposed between the underlayer and the overlayer, said magneticrecording media comprising: a layer means for providing a first stack inlaminar contact with a second stack, wherein said first stack has afirst magnetocrystalline anisotropy greater than a secondmagnetocrystalline anisotropy of said second stack; and wherein saidfirst stack has a first Curie temperature smaller than a second Curietemperature of said second stack.
 59. The magnetic recording diskrecited in claim 58, wherein the first Curie temperature of the firststack is in the range of 100-350° C. lower than the second Curietemperature of the second stack.
 60. A magnetic recording diskcomprising: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a layer means for providing a first stack having a first Curietemperature and a first magneto-crystalline anisotropy; a layer meansfor providing a second stack having a second Curie temperature largerthan the first Curie temperature and a second magneto-crystallineanisotropy having a magnitude smaller than the first magneto-crystallineanisotropy; and a spacer layer disposed between the first stack and thesecond stack.
 61. The magnetic recording disk recited in claim 60,wherein the first Curie temperature of the first stack is in the rangeof 100-350° C. lower than the second Curie temperature of the secondstack.
 62. A disk drive system, comprising: a magnetic recording diskincluding: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a first stack comprising a plurality of repetitions of first magneticlayers interleaved with first nonmagnetic layers, wherein said firststack has a first Curie temperature and a first magneto-crystallineanisotropy; and a second stack comprising a plurality of repetitions ofsecond magnetic layers interleaved with second nonmagnetic layers, saidsecond stack in laminar contact with said first stack, and wherein saidsecond stack has a second Curie temperature greater than said firstCurie temperature and said second stack has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy; a magnetic read/write head formagnetically recording data on the magnetic recording disk; an actuatorfor moving said read/write head across the magnetic disk so that theread/write head may access different regions of the magnetic recordingdisk; and a recording channel coupled electrically to the write head formagnetically recording data on the magnetic recording disk and to themagnetoresistive sensor of the read head for detecting changes in theresistance of the magnetoresistive sensor in response to magnetic fieldsfrom the magnetically recorded data.
 63. The disk drive system recitedin claim 62, wherein said first magnetic layers are chosen from a groupof materials consisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb,Co—Pd—Cr—Nb, Co—Pd—Cr—B and Co—Pd—Cr.
 64. The disk drive system recitedin claim 62, wherein said second magnetic layers are chosen from a groupof materials consisting of Co, Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb,Co—Pd—Cr—Nb, Co—Pd—Cr—B and Co—Pd—Cr.
 65. The disk drive system recitedin claim 62, wherein said first nonmagnetic layers are made of platinumor palladium.
 66. The disk drive system recited in claim 62, whereinsaid second nonmagnetic layers are made of platinum or palladium.
 67. Adisk drive system, comprising: a magnetic recording disk including: asubstrate; an underlayer adjacent to the substrate; an overlayer; and amagnetic recording media disposed between the underlayer and theoverlayer, said magnetic recording media comprising: a first magneticlayer made of a granular L1₀ phase of Fe—Pt or Co—Pt alloys, whereinsaid first magnetic layer has a first Curie temperature and a firstmagneto-crystalline anisotropy; and a second magnetic layer made ofCo—Pt or Co—Pd alloys, said second magnetic layer in laminar contactwith said first magnetic layer, and wherein said second magnetic layerhas a second Curie temperature greater than said first Curie temperatureand said second magnetic layer has a second magneto-crystallineanisotropy having a magnitude smaller than said firstmagneto-crystalline anisotropy; a magnetic read/write head formagnetically recording data on the magnetic recording disk; an actuatorfor moving said read/write head across the magnetic disk so that theread/write head may access different regions of the magnetic recordingdisk; and a recording channel coupled electrically to the write head formagnetically recording data on the magnetic recording disk and to themagnetoresistive sensor of the read head for detecting changes in theresistance of the magnetoresistive sensor in response to magnetic fieldsfrom the magnetically recorded data.
 68. The disk drive system recitedin claim 67, wherein said first magnetic layer is made of Fe—Pt—Ni. 69.The disk drive system recited in claim 67, wherein the second magneticlayer is made of Co—Pt—Cr.
 70. A disk drive system, comprising: amagnetic recording disk including: a substrate; an underlayer adjacentto the substrate; an overlayer; and a magnetic recording media disposedbetween the underlayer and the overlayer, said magnetic recording mediacomprising: a first magnetic layer made of a granular L1₀ phase of Fe—Ptor Co—Pt alloys, wherein said first magnetic layer has a first Curietemperature and a first magneto-crystalline anisotropy; and a stackcomprising a plurality of repetitions of second magnetic layersinterleaved with nonmagnetic layers, said stack in laminar contact withsaid first magnetic layer, wherein said stack has a second Curietemperature greater than said first Curie temperature and wherein saidstack has a second magneto-crystalline anisotropy smaller than saidfirst magneto-crystalline anisotropy; a magnetic read/write head formagnetically recording data on the magnetic recording disk; an actuatorfor moving said read/write head across the magnetic disk so that theread/write head may access different regions of the magnetic recordingdisk; and a recording channel coupled electrically to the write head formagnetically recording data on the magnetic recording disk and to themagnetoresistive sensor of the read head for detecting changes in theresistance of the magnetoresistive sensor in response to magnetic fieldsfrom the magnetically recorded data.
 71. The disk drive system recitedin claim 70, wherein the first magnetic layer is made of Fe—Pt—Ni. 72.The disk drive system recited in claim 70, wherein said second magneticlayers are chosen from a group of materials consisting of Co,Co—Pt—Cr—B, Co—Pt—Cr, Co—Cr, Cr—Pt—Cr—Nb, Co—Pd—Cr—Nb, Co—Pd—Cr—B andCo—Pd—Cr.
 73. The disk drive system recited in claim 70, wherein saidnonmagnetic layers are made of platinum or palladium.
 74. A disk drivesystem, comprising: a magnetic recording disk including: a substrate; anunderlayer adjacent to the substrate; an overlayer; and a magneticrecording media disposed between the underlayer and the overlayer, saidmagnetic recording media comprising: a first magnetic layer having afirst magneto-crystalline anisotropy and a first Curie temperature; anda second magnetic layer having a second magneto-crystalline anisotropyand a second Curie temperature, wherein said second magneto-crystallineanisotropy is smaller than said first magneto-crystalline anisotropy andsaid second Curie temperature is greater than said first Curietemperature, and wherein said second magnetic layer is in laminarcontact with said first magnetic layer; a magnetic read/write head formagnetically recording data on the magnetic recording disk; an actuatorfor moving said read/write head across the magnetic disk so that theread/write head may access different regions of the magnetic recordingdisk; and a recording channel coupled electrically to the write head formagnetically recording data on the magnetic recording disk and to themagnetoresistive sensor of the read head for detecting changes in theresistance of the magnetoresistive sensor in response to magnetic fieldsfrom the magnetically recorded data.
 75. The disk drive system asrecited in claim 74, wherein said first magnetic layer is chosen from agroup of materials consisting of Fe—Pt, Fe—Pt—Ni, Co—Pt and Co—Pd. 76.The disk drive system as recited in claim 74, wherein said secondmagnetic layer is chosen from a group of materials consisting of Co—Pt,Co—Pt—Cr, Co—Pt—Cr—Nb, Co—Pt—Cr—B, Co—Pd, Co—Pd—Cr, Co—Pd—Cr—Nb andCo—Pd—Cr—B.
 77. A disk drive system, comprising: a magnetic recordingdisk including: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a layer means for providing a first stack in laminar contact with asecond stack, wherein said first stack has a first magnetocrystallineanisotropy greater than a second magnetocrystalline anisotropy of saidsecond stack; and wherein said first stack has a first Curie temperaturesmaller than a second Curie temperature of said second stack; a magneticread/write head for magnetically recording data on the magneticrecording disk; an actuator for moving said read/write head across themagnetic disk so that the read/write head may access different regionsof the magnetic recording disk; and a recording channel coupledelectrically to the write head for magnetically recording data on themagnetic recording disk and to the magnetoresistive sensor of the readhead for detecting changes in the resistance of the magnetoresistivesensor in response to magnetic fields from the magnetically recordeddata.
 78. A disk drive system, comprising: a magnetic recording diskincluding: a substrate; an underlayer adjacent to the substrate; anoverlayer; and a magnetic recording media disposed between theunderlayer and the overlayer, said magnetic recording media comprising:a layer means for providing a first stack having a first Curietemperature and a first magneto-crystalline anisotropy; a layer meansfor providing a second stack having a second Curie temperature largerthan the first Curie temperature and a second magneto-crystallineanisotropy having a magnitude smaller than the first magneto-crystallineanisotropy; and a spacer layer disposed between the first stack and thesecond stack; a magnetic read/write head for magnetically recording dataon the magnetic recording disk; an actuator for moving said read/writehead across the magnetic disk so that the read/write head may accessdifferent regions of the magnetic recording disk; and a recordingchannel coupled electrically to the write head for magneticallyrecording data on the magnetic recording disk and to themagnetoresistive sensor of the read head for detecting changes in theresistance of the magnetoresistive sensor in response to magnetic fieldsfrom the magnetically recorded data.